1. Field of the Invention
This invention relates to a thin film magnetic head, a magnetic head device and a magnetic disk driving device.
2. Related Art Statement
A floating type thin film magnetic head includes usually a writing element constructed of an inductive type electromagnetic conversion element and a reading element constructed of a magnetoresistive effective element. The inductive type electromagnetic conversion element is covered with a protection film which is made of an inorganic insulating material such as alumina and constitutes an outermost surface layer of the magnetic head in the air outflow side.
The inductive type electromagnetic conversion element includes a first and a second magnetic films, a gap film, a coil film and an insulating film, etc. The edge portions of the first and second magnetic films, which are opposed each other via the gap film in the air bearing surface (hereinafter, called as “ABS”) of the slider, constitutes a pole portion for writing.
Moreover, the second magnetic film rises up with inclination of a given angle on the gap film, extending backward from the ABS with maintaining a minute space for the first magnetic film, and is joined with the first magnetic film.
The coil film passes through the space (inner gap) in between the first and the second magnetic films and winds spirally around a backward joined portion between the first and the second magnetic films. Both ends of the coil film are drawn out to the outside via a terminal conductor bump. The inner gap in between the first and the second magnetic films is filled by the insulating film. The coil film is embedded in the insulating film. The second magnetic film is formed on the insulating film.
In writing for a magnetic disk by the above thin film magnetic head, an electric current for writing is supplied to the coil film of the inductive type electromagnetic conversion element.
In this case, however, the coil film develop a heat. As mentioned above, since the coil film is embedded in the insulating film made of an organic insulating material, and the insulating film is covered with the protection film made of alumina, etc., the coil film can not radiate the heat effectively. Therefore, the developed heat is stored in the thin film magnetic head, and thus, expands the insulating film thermally.
The thermally expanded insulating film presses and expands the protection film to the outside. The expansion of the protection film influences the ABS, resulting in the expansion of the inductive type electromagnetic conversion element in the ABS. Moreover, the developed heat in the coil film expands the first and the second magnetic films adjacent to the insulating film thermally. As a result, the edge of the pole portion, not much strongly fixed, composed of the first and the second magnetic films is expanded in the ABS side. The expansion degree often reaches 10 nm.
In a magnetic disk driving device having such a thin film magnetic head, for high recording density, the floating space between the ABS of the thin film magnetic head and a magnetic disk is narrowed gradually to 40 nm, 30 nm, 20 nm or 10 nm. Therefore, the above expansion in the ABS can easily crash the thin film magnetic head itself and the magnetic disk or damage the magnetic recorded data, resulting in the deterioration of the reliability of the magnetic disk driving device.
For resolving the problem, Japanese Laid-open Patent Publication Kokai Hei 4-366408 (JP A 4-366408) discloses that a recessed portion is formed on the surface of a protection film made of an inorganic material in a medium opposing surface. The recessed portion is so formed that the surface of the protection film is polished flat with heating the thin film magnetic head element and thereby, expanding the protection film.
However, the disclosed technique dose not repress the thermal expansion of the protection film, but allows the thermal expansion as far as the protection film does not expands beyond the flat ABS by retreating the protection film from the ABS in advance. Therefore, the disclosed technique can not solve the above problem.
Moreover, in the above technique, the complicate process is required that the protection film is flattened on the basis of the assumed expansion degree due to the developed heat at a recording operation. In addition, the configuration of the slider, particularly the geometrical shape of the ABS is specified to a give shape, and thus, the ABS can not have another geometrical shape for improving the floating performance. Then, in the above technique, a means to repress the thermal expansion of the edge of the pole portion is not disclosed.